1,2-bis(2,2-difluoroethoxy)ethane and manufacturing method thereof

ABSTRACT

1,2-Bis(2,2-difluoroethoxy)ethane which can be used as electrolyte solution of a non-aqueous electrolyte secondary battery is provided. Used are 1,2-Bis(2,2-difluoroethoxy)ethane represented by the following formula (1): 
     
       
         
         
             
             
         
       
     
     and a method for manufacturing 1,2-bis(2,2-difluoroethoxy)ethane including the step of reacting 2-(2,2-difluoroethoxy)ethanol represented by the following formula (2) with a compound represented by the general formula (3) in a basic compound or a basic compound-containing solvent: 
     
       
         
         
             
             
         
       
     
     wherein Lg represents an anionic leaving group.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to 1,2-bis(2,2-difluoroethoxy)ethane whichcan be used as electrolyte solution of a non-aqueous electrolytesecondary battery.

2. Description of the Related Art

A non-aqueous electrolyte secondary battery has a higher voltage and ahigher energy density in comparison with a secondary battery includingan aqueous electrolyte solution. A non-aqueous solvent includingfluorinated dialkoxyethane is effective for improving the power outputand the oxidation resistance, due to having a small viscosity. Among thesolvent, CH₃OCH₂CH₂OCH₂CF₃ is supposed to be a suitable non-aqueoussolvent, having a low viscosity and a high relative permittivity (see,for example, Japanese Patent Laid-Open No. 1-117838). Further, physicalproperties of CH₃OCH₂CH₂OCH₂CF₃ and CH₃CH₂OCH₂CH₂OCH₂CF₃ relating toproperties as electrolyte solution are described (see, for example, G.Shimazaki et al., “Physical properties of trifluorodialkoxyethane andproperties of electrolyte solution”, Proceedings of the 73rd Meeting ofthe Electrochemical Society of Japan (Apr. 1, 2006), p. 242).

Since the presence of halide ions such as chlorine ions in electrolytesolution of a lithium ion secondary battery usually causes substantialdegradation of the battery properties, the halide ion content is desiredto be as low as possible.

In general, a fluorine-containing alkoxy metal salt and an ethercompound substituted with a leaving group are used for synthesizing afluorine-containing glyme compound which can be used as the electrolytesolution of a non-aqueous electrolyte battery (see, for example,Japanese Patent Laid-Open No. 2010-241772). In the case of a halogenleaving group, the halide ions are contained in the reaction residue. Itis therefore feared that the halide ions remain in the isolated andpurified fluorine-containing glyme compound.

SUMMARY OF THE INVENTION

Although various fluorinated glymes are described as above, any knowncompound having a 2,2-difluoroethoxy group (CF₂HCH₂O—) has thefunctional group on one terminal only. In contrast,1,2-bis(2,2-difluoroethoxy)ethane(CF₂HCH₂OCH₂CH₂OCH₂CF₂H) of the presentinvention, which has 2,2-difluoroethoxy groups on both terminals, is anovel compound which has not been manufactured before.

In synthesis of the novel compound of the present invention, forexample, for use as electrolyte solution, the use of a compoundsubstituted with a halogen is required to be avoided to the utmost inorder to prevent reduction in battery properties.

Through extensive investigation, the present inventors have found1,2-bis(2,2-difluoroethoxy)ethane which can be used as electrolytesolution of a non-aqueous electrolyte secondary battery, and adopted amanufacturing method using no compound substituted with a halogen, sothat the present invention has been accomplished.

More specifically, the present invention relates to1,2-bis(2,2-difluoroethoxy)ethane represented by the following formula(1):

and further relates to a method for manufacturing1,2-bis(2,2-difluoroethoxy)ethane including reacting2-(2,2-difluoroethoxy)ethanol represented by the following formula (2):

with a compound represented by the following general formula (3):

wherein Lg represents an anionic leaving group.

Through extensive investigation of the synthesis of1,2-bis(2,2-difluoroethoxy)ethane of the present invention, it was foundthat 1,2-bis(2,2-difluoroethoxy)ethane having a less final content ofhalide ions can be manufactured through incorporation of the step ofsynthesizing 2-(2,2-difluoroethoxy)ethanol having an extendedoxyethylene chain by using ethylene carbonate, thereby accomplishing thepresent invention.

According to the present invention, a novel compound1,2-bis(2,2-difluoroethoxy)ethane which can be used as an electrolytesolution of non-aqueous electrolyte secondary battery can be synthesizedand provided. Further, according to the manufacturing method of thepresent invention, 1,2-bis(2,2-difluoroethoxy)ethane can be synthesizedto have a halide ion content of less than 10 ppm by weight, which isindustrially useful in application to an electrolyte solution and thelike.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in more detail in the following.

1,2-Bis(2,2-difluoroethoxy)ethane of the present invention isrepresented by the following formula (1):

1,2-Bis(2,2-difluoroethoxy)ethane can be synthesized by reacting2-(2,2-difluoroethoxy)ethanol represented by the following formula (2):

with a compound represented by the following general formula (3):

in a basic compound or a basic compound-containing solvent, wherein Lgrepresents an anionic leaving group.

In manufacturing 1,2-bis(2,2-difluoroethoxy)ethane of the presentinvention, the anionic leaving group (referred to as Lg) is preferablyother than halogens. Any reactive group may be used, and particularlypreferred examples include a p-toluene sulfonyloxy group (p-CH₃C₆H₄SO₃—)and a trifluoromethane sulfonyloxy group (CF3SO₃—). The amount used of acompound represented by the formula (3) may be 1.0 times or more,preferably 1.1 times to 2.0 times, the moles of2-(2,2-difluoroethoxy)ethanol for use in the reaction.

Examples of the basic compound for use in manufacturing1,2-bis(2,2-difluoroethoxy)ethane of the present invention includelithium hydride, sodium hydride, potassium hydride, calcium hydride,metallic sodium, butyl lithium, lithium diisopropylamide, lithiumhydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide,sodium carbonate, potassium carbonate, triethylamine, pyridine,picoline, lutidine and sodium amide. In the case of a basic compoundcreating water as byproduct in forming an alkoxy salt, reduction inyield is feared. Accordingly, lithium hydride, sodium hydride, potassiumhydride, calcium hydride, butyl lithium, and lithium diisopropylamidemay be preferably used in an amount of 1.0 times or more, preferably 1.1times to 2.0 times, the moles of 2-(2,2-difluoroethoxy)ethanol for usein the reaction.

In manufacturing 1,2-bis(2,2-difluoroethoxy)ethane of the presentinvention, examples of the solvent for use in the reaction includediethyl ether, methyl tertiary butyl ether, tetrahydrofuran, diisopropylether, di-n-butyl ether, dioxane, dioxolane, dimethyl sulfoxide,acetonitrile, pyridine, picoline, lutidine, and collidine, which may beused in an amount of 2.0 parts to 40.0 parts, preferably 5.0 parts to15.0 parts relative to 2-(2,2-difluoroethoxy)ethanol for use in thereaction.

In the reaction for manufacturing 1,2-bis(2,2-difluoroethoxy)ethane ofthe present invention, 2-(2,2-difluoroethoxy)ethanol represented by theformula (2) may be dripped into a mixture previously prepared from abasic compound, a solvent, and a compound represented by the formula(3), or the dripping sequence of 2-(2,2-difluoroethoxy)ethanolrepresented by the formula (2) and the compound represented by theformula (3) may be inverted. The reaction may be performed at −20° C. to50° C., preferably in the range from 5° C. to 30° C., and morepreferably in the range from the melting point or more of a solvent foruse to 30° C. in the case of the solvent with a high melting point.

In manufacturing of 1,2-bis(2,2-difluoroethoxy)ethane of the presentinvention, the synthesis of 2-(2,2-difluoroethoxy)ethanol represented bythe formula (2)is performed preferably without using a compoundsubstituted with a halogen. More specifically,2-(2,2-difluoroethoxy)ethanol can be obtained by heating2,2-difluoroethanol and ethylene carbonate in the presence of a basiccompound.

Ethylene carbonate for use in the reaction of 2,2-difluoroethanol andethylene carbonate may be used in an amount of 0.1 times or more themoles of 2,2-difluoroethanol for use in the reaction. With an amount ofless than 0.05 times the moles, the reaction time may be extended insome cases, which is inefficient. With an amount of more than 2.0 timesthe moles, a large amount of remaining ethylene carbonate may causedifficulty in purification procedure in some cases. Accordingly theamount used may be preferably 0.2 times the moles to 1.2 times themoles.

Examples of the basic compound for use in the reaction of2,2-difluoroethanol and ethylene carbonate include trimethylamine,triethylamine, triisopropylamine, tributylamine, sodium carbonate,potassium carbonate, and cesium carbonate, though not particularlylimited thereto.

The reaction solvent for the reaction of 2,2-difluoroethanol andethylene carbonate is used on an as needed basis, though the reactionmay be performed without using the solvent. In the case of using areaction solvent, examples of the reaction solvent include hexane,heptane, toluene, benzene, cumene, and xylene, though not particularlylimited thereto. The amount of the reaction solvent is 10 parts or less,more preferably 1 part or less, relative to 2,2-difluoroethanol for usein the reaction. Alternatively, in the case of using an amine such astrimethylamine and triethylamine as base, the amine may be used as asubstitute for solvent.

The reaction temperature for the reaction of 2,2-difluoroethanol andethylene carbonate is preferably from 80° C. to the boiling point orless of a solvent for use. In the case of using an organic base as thebase, the reaction is performed preferably at the boiling point thereofor less. In the case of using a solvent having a boiling point less than80° C. under normal pressure, the reaction is preferably performed at80° C. or more under pressure.

In the post-processing after the reaction for obtaining1,2-bis(2,2-difluoroethoxy)ethane of the present invention, purificationcan be performed by concentration and distillation after stopping thereaction with water in a necessary quantity. The amount of water may bethe difference in moles between a basic compound and2-(2,2-difluoroethoxy)ethanol for use in the reaction. After thereaction of 2,2-difluoroethanol with ethylene carbonate, concentrationor distillation is directly performed, so that2-(2,2-difluoroethoxy)ethanol can be purified. Alternatively2-(2,2-difluoroethoxy)ethanol may be directly used in the subsequentprocess without purification.

Examples of the halide ions which may possibly be contained in1,2-bis(2,2-difluoroethoxy)ethane of the present invention includechlorine ions, bromine ions and iodine ions. The content of these halideions may be simply and accurately measured by a known method such aspotentiometric titration.

The content of halide ions (total amount of chlorine ions, bromine ionsand iodine ions) in the 1,2-bis(2,2-difluoroethoxy)ethane of the presentinvention is preferably less than 10 ppm. With a content of halide ionsof 10 ppm or more, an adverse effect on the battery performance, forexample, degradation of the battery properties, may be brought inrepeated charging/discharging of the battery in some cases. Though thereason is not clear, phenomena such as the elution of electrode activematerial and the progress of corrosion of Al or the like for use ascurrent collector of an electrode in the presence of halide ions may bepossibly involved.

EXAMPLES

In the following, synthesis of 1,2-bis(2,2-difluoroethoxy)ethane of thepresent invention will be more specifically described with reference toexamples, but the present invention is not limited to the examples. Inthe analysis, the following instruments were used:

-   -   ¹H-NMR and ¹⁹F-NMR: AVANCE II 400 manufactured by Bruker        Corporation;    -   GC-MS: GCMS-QP2010 Plus manufactured by SHIMADZU CORPORATION;        and    -   Potentiometric titration: Automatic potentiometric titrator        AT-610 manufactured by Kyoto Electronics Manufacturing Co., Ltd.

Example 1

A 200-ml three neck flask having a stirring bar was charged with 3agents including 2,2-difluoroethanol (34.0 g, 0.41 mol), ethylenecarbonate (54.8 g, 0.62 mol), and triethylamine (42.0 g, 0.41 mol), andthe mixture was stirred at 95° C. for 24 hours after substitution withnitrogen. The reaction liquid was cooled to room temperature and thereaction yield of 2-(2,2-difluoroethoxy)ethanol was determined to be 70%by ¹H-NMR. By a subsequent conventional purification procedure,2-(2,2-difluoroethoxy)ethanol (31.5 g, 0.25 mol) was obtained.

Subsequently, a 2000-ml three neck flask having a stirring bar wascharged with 60% sodium hydride (21.2 g, 0.53 mol), dimethyl sulfoxide(375.2 g), and 2,2-difluoroethyl tosylate (100.0 g, 0.42 mol, HF₂CCH₂OTsin the formula (4)) under nitrogen stream. The mixture was cooled to 10°C. or less, and 2-(2,2-difluoroethoxy)ethanol (31.5 g, 0.25 mol) wasthen slowly dripped therein. The mixture was then stirred at roomtemperature for 16 hours and quenched with addition of water afterreaction. The reaction yield of 1,2-bis(2,2-difluoroethoxy)ethane wasdetermined to be 72% by ¹⁹F-NMR of the quenched mixture. Through asubsequent conventional purification procedure, 30.4 g of1,2-bis(2,2-difluoroethoxy)ethane was obtained (yield: 64%). Analyticalresults were as follows. In the NMR analysis, a TMS-containing solventfor measurement was used, and the chemical shift in ¹H-NMR wascorrected. In ¹⁹F-NMR, hexafluorobenzene (−162 ppm) was used as internalstandard for correction of the chemical shift.

¹H-NMR (MeOD-d4, 400 MHz): 3.69 ppm (dt, 4H, CH₂), 3.71 ppm (s, 4H,OCH₂CH₂O), 5.85 ppm (tt, 2H, CHF₂);

¹⁹F-NMR (MeOD-d4, 400 MHz): −126.1 ppm (dt, 4F, CHF₂); Boiling point (b.p.): 62-63° C. (10 mmHg);

GC-MS (m/z): 170 (m-20, 5), 139 (9), 109 (50), 95 (79), 65 (100), 45(51), 43 (23), 31 (19).

In GC-MS, though no molecular ion peak was confirmed, de-HF (m-20) wasobserved. The content of halide ions was determined to be 0.3 ppm(detection limit: 0.1 ppm) by potentiometric titration.

Example 2

The dripping sequence of 2-(2,2-difluoroethoxy)ethanol and2,2-difluoroethyl tosylate in Example 1 was inverted in implementation.As a result, the reaction yield of 1,2-bis(2,2-difluoroethoxy)ethane was65%. The yield of 2-(2,2-difluoroethoxy)ethanol as precursor compoundwas 70%, similarly as in Example 1. The content of halide ions wasdetermined to be 0.4 ppm (detection limit: 0.1 ppm) by potentiometrictitration.

Examples 3 to 5

Examples of synthesis of 1,2-bis(2,2-difluoroethoxy)ethane performed inthe same way as in Example 1, except only that the basic compound inExample 1 for converting 2-(2,2-difluoroethoxy)ethanol into a metal saltwas changed, are described in the following. The detection limit of thecontent of halide ions was 0.1 ppm.

TABLE 1 Basic compound Yield Halide ion content Example 3 Potassiumhydride (30 wt 69% 0.3 ppm % in mineral oil) Example 4 n-Butyl lithium(1.6M 51% 0.7 ppm n-hexane solution) Example 5 Potassium hydroxide 39%0.9 ppm

Example 6

Synthesis of 1,2-bis(2,2-difluoroethoxy)ethane was performed in the sameway as in Example 1, except that 2,2-difluoroethyl triflate (HF₂CCH₂OTfin the formula (5)) was used instead of 2,2-difluoroethyl tosylate inExample 1. The reaction yield of 1,2-bis(2,2-difluoroethoxy)ethane wasdetermined to be 70% by ¹⁹F-NMR after reaction. The content of halideions was determined to be 0.5 ppm (detection limit: 0.1 ppm) bypotentiometric titration.

Comparative Example 1

A 100-ml three neck flask having a stirring bar was charged with 60%sodium hydride (4.2 g, 0.11 mol) and dimethylsulfoxide (75.0 g) undernitrogen stream. The mixture was cooled to 10° C. or less, and2,2-difluoroethanol (9.0 g, 0.11 mol) was then slowly dripped therein.The mixture was stirred at 10° C. or less for 2 hours and 2-bromoethanol(13.7 g, 0.11 mol) was then slowly dripped therein. The mixture wasstirred at room temperature for 4 hours and quenched with addition ofwater after reaction. The reaction yield of2-(2,2-difluoroethoxy)ethanol was determined to be 60% by ¹⁹F-NMR of themixture. Through a subsequent conventional purification procedure,2-(2,2-difluoroethoxy)ethanol was obtained (6.6 g, 0.052 mol, isolatedyield: 47%).

Subsequently, 1,2-bis(2,2-difluoroethoxy)ethane was synthesized in thesame way as in Example 1, using the obtained2-(2,2-difluoroethoxy)ethanol, with a reaction yield of 68% and anisolated yield of 58%. The content of halide ions was determined to be70.3 ppm (detection limit:

0.1 ppm) by potentiometric titration.

According to the present invention, a novel compound1,2-bis(2,2-difluoroethoxy)ethane becomes available. Further, accordingto the manufacturing method of the present invention, a compound havinga low halogen content can be produced, so that1,2-bis(2,2-difluoroethoxy)ethane which can be used as electrolytesolution of a non-aqueous electrolyte secondary battery becomesavailable.

What is claimed is:
 1. 1,2-Bis(2,2-difluoroethoxy)ethane represented bythe following formula (1):


2. 1,2-Bis(2,2-difluoroethoxy)ethane according to claim 1, wherein acontent of halide ions (total amount of chlorine ions, bromine ions andiodine ions) is less than 10 ppm by weight.
 3. A method formanufacturing 1,2-bis(2,2-difluoroethoxy)ethane according to claim 1comprising the step of reacting 2-(2,2-difluoroethoxy)ethanolrepresented by the following formula (2):

with a compound represented by the general formula (3):

in a basic compound or a basic compound-containing solvent, wherein Lgrepresents an anionic leaving group.
 4. The method for manufacturing1,2-bis(2,2-difluoroethoxy)ethane according to claim 3, wherein thebasic compound comprises at least one selected from the group consistingof lithium hydroxide, sodium hydroxide, potassium hydroxide, calciumhydroxide, lithium hydride, sodium hydride, potassium hydride, calciumhydride, metallic sodium, butyl lithium, lithium diisopropylamide,sodium carbonate, potassium carbonate, triethylamine, pyridine,picoline, and lutidine.
 5. The method for manufacturing1,2-bis(2,2-difluoroethoxy)ethane according to claim 3, wherein thebasic compound comprises at least one selected from the group consistingof lithium hydride, sodium hydride, potassium hydride, calcium hydride,butyl lithium, and lithium diisopropylamide.
 6. The method formanufacturing 1,2-bis(2,2-difluoroethoxy)ethane according to claim 3,wherein the leaving group Lg in the general formula (3) is a p-toluenesulfonyloxy group (p-CH₃C₆H₄SO₃—) or a trifluoromethane sulfonyloxygroup (CF₃SO₃—).
 7. The method for manufacturing1,2-bis(2,2-difluoroethoxy)ethane according to claim 6, wherein thesynthesis step of 2-(2,2-difluoroethoxy)ethanol represented by theformula (2) comprises reacting 2,2-difluoroethanol with ethylenecarbonate.